Computer repair is much more than just taking things apart and putting them back together. It requires the use of tools, spare parts, and components for testing and repairs. This process involves a lot of diagnostic tests and, of course, a lot of waiting until those tests are finished. Unfortunately, there is no way to predict what problems a computer will have and how long they will take to repair.
In addition, repeated attempts to recover data can significantly increase the time needed to repair a computer.